Porous metal based composite material

ABSTRACT

A porous composite material includes a metal material for forming a matrix, and at least two kinds of fine particle materials having different wettabilities with respect to the metal material. The porous composite material is provided by melting and impregnating the metal material for forming a matrix with the mixture of at least two kinds of fine particle materials. The porous composite material has excellent characteristics in shock absorbency, acoustics, non-combustibility, lightness, rigidity, and so forth.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a porous metal based compositematerial which requires no pressuring mechanism during manufacture dueto the spontaneous penetration of a metal which will become a matrix, orwhich can be manufactured under low pressure even if pressure isrequired, and the characteristic control thereof.

[0003] 2. Description of the Related Art

[0004] Known methods of manufacturing porous materials include: (1)powder metallurgy to sinter metal powder or short fibers; (2) method tofoam by directly adding a foam material to molten metal; (3) method toremove plastic after plating on foam plastic; (4) method to compound amaterial having a small density, such as a foam material, with a metal;(5) method to blow gas into molten metal under zero gravity; and soforth.

[0005] However, in consideration of these methods, including the aspectof making a metal-based composite material porous, the method (1) ispowder metallurgy and is thus uneconomical although the manufacture ofTi or Ti alloy stainless steel has been attempted. As an example of themethod (2), Al alloy is foamed by using hydride such as Ti and Zr. Inthis method, it is difficult to select a foam material for a steelmaterial. It is also difficult to provide an even structure in thismethod by foaming a composite material of metal and non-metal or thelike. In the method (3), plastic as an organic material is partiallyused, so that the application thereof is limited, which is troublesome.As an example of the method (4), Al alloy and Shirasu balloon-pumice arecompounded. However, since hot molten metal has to be pressured andinjected into an inorganic material having a small density, there arerestrictions on a manufacturing facility. The method (5) has adifficulty in mass-production.

[0006] On the other hand, the present inventors discovered theapplication of a hard brazing material for a base which has littlerestriction on the types, shapes and the like of joining members andwhich can be joined in various ways. By adding a fine particle materialto the hard brazing material to lower thermal stress, an appropriatebonding strength is kept between different members. Joining strengtharound a joining interface is not lowered even by thermal stress duringcooling after joining at high temperature, and also no cracks are formedat weak members by thermal stress during cooling, so that it was foundthat two or more different members can be joined. In other words, thepresent inventors found that the above-noted properties can be obtainedby an adhesive composition for bonding two or more different members.The adhesive composition consists of at least two types of fine particlematerials having different wettabilities with respect to the hardbrazing material, and the hard brazing material. The present inventorsthus applied Japanese Patent Application No. 11-300184 as of Oct. 21,1999. However, since this invention focuses on joining, there was notenough examination concerning the specific thickness of the adhesivecomposition or the application of the adhesive composition as a memberitself at the time of the application.

SUMMARY OF THE INVENTION

[0007] Accordingly, it is an object of the present invention to providea porous composite material which has an excellent coefficient ofthermal expansion, Young's modulus, proof stress and so forth, and inparticular, a porous composite material that is simple for industrialapplications and can be economically manufactured.

[0008] It is effective to make a material porous by controllingmechanical properties and physical properties. A porous material hasexcellent characteristics as a functional material, including shockabsorbency, acoustic characteristics, non-combustibility, lightweight,rigidity and so forth, and a wide range of applications is expected. Forinstance, the material may be a shock absorbing material for theinterior and exterior of a vehicle. As a building material, thesound-absorbing property, in addition to being non-combustible andlightweight, can also be expected. Then, the applicability of theadhesive composition was examined not only as an adhesive composition tofill in the gaps of joining materials but also as a large member productand as a porous material of the member. When molten metal permeates intothe mixture of fine particle materials having different wettabilitieswith respect to the molten metal, it is necessary to provide a fixed orhigher level of penetration force by choosing the conditions of a matrixmetal, fine particle material and so forth. Additionally, the powderhaving different wettabilities is mixed to provide an evenly porousmaterial. Thus, it was found that a member having a desirable size canbe manufactured and an effective porous composite material can beobtained.

[0009] While focusing on this fact, the present inventors carried outvarious tests in order to solve the above-noted problems. Accordingly, aporous metal material includes a metal material for forming a matrix andat least two fine particle materials having different wettabilities withrespect to the metal material, and is provided by melting andimpregnating the metal material into the mixture of at least two fineparticle materials. The inventors found that the porous metal materialis a composite material having an excellent balance of mechanical andphysical characteristics that are different from those of the matrixmetal, for instance, a characteristic balance between a low expansioncoefficient and low proof stress, and so forth, thus completing thepresent invention.

[0010] In other words, it was found that a porous metal material isprovided by using a specific metal material as a matrix and by meltingand impregnating the metal material to fine particle materials which canlower thermal stress, thus forming a composite. The porous metalmaterial can achieve the above-noted properties as a material havingexcellent physical and mechanical characteristics because of the metalmaterial as a matrix, the fine particle material that has superiorwettability with respect to the metal material and can lower thermalstress, and holes that are formed by particles having inferiorwettability with respect to the metal material, thereby achieving thepresent invention.

BRIEF DESCRIPTION OF THE DRAWINGS

[0011]FIG. 1 is an optical microscopic photograph, showing themicrostructure of a composite material in which aluminum alloy A5005penetrated and solidified in a plated fine particle material (aluminahaving the average particle size of 50 μm);

[0012]FIG. 2 is an optical microscopic photograph, showing themicrostructure of a composite material in which aluminum alloy A5005penetrated and solidified in particles where a plated fine particlematerial (alumina having the average particle size of 50 μm) and anon-plated fine particle material (alumina having the average particlesize of 50 μm) were mixed at 2:1; and

[0013]FIG. 3 is an optical microscopic photograph, showing themicrostructure of a composite material in which aluminum alloy A5005penetrated and solidified in particles where a plated fine particlematerial (alumina having the average particle size of 50 μm) and anon-plated fine particle material (alumina having the average particlesize of 50 μm) were mixed at 1:2.

DESCRIPTION OF THE PREFERRED EMBODIMENT

[0014] According to a first aspect of the present invention, the presentinvention relates to a porous metal based composite material whichincludes a metal material for forming a matrix and at least two kinds offine particle materials having different wettabilities with respect tothe metal material, and which is provided by melting and impregnatingthe at least two kinds of fine particle materials to the metal material.

[0015] It is preferable that the metal material for forming a matrix isAu, Ag, Cu, Pd, Al, Fe, Cr, Co or Ni, or an alloy containing thesemetals as a main component. Moreover, the mixture of at least two kindsof fine particle materials having different wettabilities with respectto the metal material is preferably the mixture of surface treatedceramic fine particles, cermet fine particles or metal fine particlesand surface untreated ceramic fine particles, cermet fine particles ormetal fine particles. Furthermore, it is preferable that the mixture ofat least two kinds of fine particle materials having differentwettabilities with respect to the metal material contains the surfaceuntreated fine particle material and the surface treated fine particlematerial at the volume ratio of 80:20 to 5:95. Additionally, a secondaspect of the present invention relates to the application of theabove-noted porous metal based composite material as a shock-absorbingmaterial, a vibration-absorbing material or a sound-absorbing material.

[0016] Combinations of a material having superior wettability withrespect to the metal material and a material having inferior wettabilitywith respect to the metal material, for example, include ceramic fineparticles that are surface treated by such as plating and ceramic fineparticles that are not surface treated; and metal fine particles thatare surface treated by such as plating or that are not surface treated,and surface untreated ceramic fine particles; and so forth. There is noparticular limitation on a plating method. However, electroless platingis preferable.

[0017] Wettabilities with respect to the metal material can be kept evenwithout metal plating by mixing an additive such as Ti to the metalmaterial or to the fine particle materials as fine particles, and thusby forming a reaction layer of active materials such as nitride, oxideand carbide on a ceramic surface when the matrix material is melted andimpregnated. In this case, the above-mentioned effects can be obtainedby combining materials having different wettabilites with respect to themetal material containing the additive. The effects can be preferablyobtained by the combination of dispersion materials, for instance,nitride and oxide or nitride and carbide. The amount of the activematerials is preferably around 0.5 to 5% in a weight ratio relative tothe amount of the metal material for forming a matrix.

[0018] Moreover, each average particle size of at least two kinds offine particle materials having different wettabilities with respect tothe metal material may be similar to each other or different from eachother. Particle sizes can also be selected over a wider range than thesizes when the materials are used as an adhesive composition. In otherwords, the mixture of at least two kinds of fine particle materialshaving different wettabilities with respect to the metal material can beeasily prepared by mixing, for instance, alumina particles that areNi-plated at about 0.3 μm and have a desirable grain size such as theaverage particle size of 50 μm as particles that are surface treated ata desirable thickness, and, for example, alumina particles that have adesirable grain size such as the average particle size of 50 μm assurface untreated particles.

[0019] Or alternatively, the mixture can be easily prepared by mixing,for instance, alumina particles that are Ni-plated at about 0.5 μm andhave a desirable grain size such as the average particle size of 50 μmas particles that are surface treated at a desirable thickness, and, forexample, Shirasu balloon particles that have a desirable grain size suchas the average particle size of 100 μm as surface untreated particles.The mixture of at least two kinds of fine particles having differentwettabilities with respect to the metal material containing Ti or thelike as an additive at a fixed amount can be easily prepared by mixing,for instance, aluminum nitride having a desirable grain size such as theaverage particle size of 50 μm and, for example, alumina particleshaving a desirable grain size such as the average particle size of 50μm.

[0020] A mixing ratio between the surface untreated fine particlematerial and the surface treated fine particle material is morepreferably 1:9. In other words, the mixing ratio of the surfaceuntreated fine particle material in all particles is about 10% to 3:1,in other words, around 75%. When the mixing ratio of the surfaceuntreated material is higher than 3:1, the metal material cannot easilypenetrate without pressure and pressurization or the like is oftenrequired, which is not preferable. Moreover, when the mixing ratio ofthe surface untreated material is lower than 1:9, the mechanicalproperty of a composite material becomes similar to that of compactfiller, which is not preferable. The composite material relating to thepresent invention may be generally manufactured in accordance with theconditions described in Japanese Patent Application No. 11-180902. Thesurface treated fine particle material does not have to be the same asthe surface untreated fine particle material. The material is good aslong as it is the combination of the surface treated fine particlematerial and the surface untreated fine particle material. In otherwords, it is unnecessary to use the same material for plated andnon-plated materials.

[0021] The metal material for forming a matrix for use in the compositematerial relating to the present invention includes pure metal such asAu, Ag, Cu, Pd, Al, Fe, Cr, Co or Ni, or an alloy having these metals asa main component. For the alloy containing these metals as a maincomponent, at least one kind of the above-noted metals may be containedas the main component. Of course, metals other than the metals mentionedabove may be contained. Appropriate metals or an alloy may be selectedfor use based on reactivity to the particles of a dispersion material ortemperature under which the composite material is used. Al alloy, forinstance, BA4004 (Al-10Si-1.5 Mg), A5005 (Al-0.8 Mg) and so forth ispreferably used since a light composite member can be obtained, andmanufacturing temperature can be low.

[0022] In melting and impregnating the pure metal or alloy material intothe particle materials, it is important to improve wettability betweenthe particles having superior wettability and molten metal in order toimprove the penetration force of the molten metal and to enlarge acomposite material to a desirable level.

[0023] Generally, the wettability of molten metal or the like isexpressed by the following Young-Dupre equation in which a drop isplaced on the surface of a solid (sessile drop method) and in which eachsurface energy is in balance at solid/liquid/gas interfaces under thefollowing condition:

γ_(SV)=γ_(S1)+γ_(1V)×cosθ

[0024] wherein θ is a contact angle; γ_(SV) is solid-gas surface energy;γ_(1V) is gas-liquid surface energy; and γ_(S1) is solid-liquid surfaceenergy.

[0025] In general, a system having good wettability is θ<90°, and asystem having poor wettability is θ>90°.In order to improve wettability(θ<90°) based on the equation mentioned above, it is necessary to setthe solid-gas surface energy γ_(SV) high and the gas-liquid surfaceenergy γ_(1V) and the solid-liquid surface energy γ_(S1) low. Thus,although an oxide film is formed on the surface of a metal which iscoated on the fine particle material having superior wettability withrespect to the molten metal during heating before melting andimpregnating the metal, the oxide has small surface energy (solid-gassurface energy γ_(SV)) and is stable, so that the wettability of thematerial coated with the oxide film thereon is poor. Therefore, when theoxide is removed in a reduction atmosphere or the like, the surfacebecomes active, having large surface energy (solid-gas surface energyγ_(SV)), and wettability increases. It is desirable to prevent oxidationunder high vacuum. It is also possible to lower the solid-gas surfaceenergy γ_(SV) to improve wettability by changing the components ofmolten liquid with an added element or the like.

[0026] Joining strength between a dispersion material dispersed in themetal material and the metal material is positively partially reduced,or fine holes are positively formed in the composite material. Thus, aporous metal based composite material provided by reducing Young'smodulus and proof stress, in addition to coefficient of thermalexpansion, can provide a cushioning effect when the material is joinedto another member having low coefficient of thermal expansion and lowfracture toughness. Additionally, a composite material having excellentheat resistance can be provided. More specifically, the effects can beachieved by mixing the dispersion material dispersed in the metalmaterial with the particles having superior wettability with respect tothe metal material, and the particles having inferior wettability withrespect to the metal material. As the mixture of the particles havingsuperior wettability and having inferior wettability with respect to themetal material, it is preferable to use particles that are surfacetreated such as by plating to keep wettability to the metal material,and particles that are not surface treated to keep wettability, ornitride and oxide, metal particles and oxide, and so forth.

[0027] When the ratio of the particles having superior wettability withrespect to the metal material is high, the microstructure of theoptically observed porous metal based composite material is not sodifferent from that of a composite material formed only of surfacetreated particles. However, the coefficient of thermal expansion andYoung's modulus of the porous material are reduced by as much as thoseof a composite material formed only of particles having superiorwettability. The proof stress of the porous material is reduced by morethan that of a composite material formed only of surface treatedparticles. This is because joining strength between the particles havinginferior wettability and the metal material is reduced in comparisonwith the particles having superior wettability. Thus, parts with theparticles having inferior wettability essentially function as holes, andit is considered that the characteristics of a composite material couldbe controlled in a desirable direction.

[0028] As the ratio of the particles having inferior wettability withrespect to the metal material increases, optically observable holes areformed in a porous metal based composite material, and the coefficientof thermal expansion declines by as much as that of a composite materialformed only of particles having superior wettability. Additionally,Young's modulus and proof stress decrease further in comparison with acomposite material having less particles with inferior wettability withrespect to the metal material. This is because the cross section of acomposite material visually decreases because of holes, in addition tothe decrease in joining strength between a dispersion material and themetal material, in the composite material with more particles havinginferior wettability with respect to the metal material. Accordingly,Young's modulus decreases, and proof stress decreases since partsadjacent to the holes or the like become crack generating points duringloading.

[0029] The effects of the porous metal based composite material relatingto the present invention were explained in accordance with the amount ofparticles that are not surface treated such as by plating to keepwettability, for the sake of convenience. However, the object, methodand effects are all the same, and it is almost unnecessary to strictlydistinguish whether or not they can be recognized as optical holes.

[0030] For the characteristic control of the composite material, it isnecessary to arrange the kinds of fine particle materials and adjust thepacking density relative to the metal material. The packing density offine particle materials relative to the metal material is 30 to 90%,preferably 40 to 70%, in volume ratios when only particles havingsuperior wettability with respect to the metal material are dispersed.The packing densities are effective in controlling the coefficient ofthermal expansion of a formed material in particular.

[0031] When the particles having superior wettability to the metalmaterial and the particles having inferior wettability to the metalmaterial are dispersed, the volume ratio of the particles is similarlyset at 30 to 90%, preferably 40 to 70%, based on the assumption that thecomposite material has no holes. It is also advantageous to increase thepacking density of the particle materials in order to lower thecoefficient of thermal expansion. However, if the packing density isincreased too much, it would be often difficult to melt and penetratematrix metal, which is not preferable. When the packing density is lowand the coefficient of thermal expansion is lower than a desirablelevel, particles cluster on one side during manufacture and ahomogeneous material is not often provided, so that attention isrequired. In other words, the coefficient of thermal expansion isadjusted by selecting the kinds of fine particle materials, or byappropriately selecting the particle size distribution of the fineparticle materials.

EXAMPLES

[0032] The present invention will be explained in further detail byreferring to examples. However, the present invention is not limited tothese examples.

Example 1

[0033] Alumina that was Ni-plated at the thickness of 0.3 μm on thesurface of particles and had the average particle size of 50 μm, andalumina that was not surface treated and had the average particle sizeof 50 μm, were mixed at each ratio of 1:0, 2:1, 1:1 and 1:2. Dispersionparticles mixed at the ratio were filled in a graphite jig.Subsequently, pure aluminum A1050 (Al >99.5%) or aluminum alloy A5005(Al-0.8 Mg) arranged on the particles melted, penetrated withoutpressure, and solidified, thus providing a composite material as asample. The mechanical and physical characteristics of the sample areshown in Table 1. In Table 1, the degree of penetration was determinedby whether or not molten metal penetrated evenly to thickness of thelayer of the dispersion particles filled in the jig.

[0034]FIG. 1, FIG. 2 and FIG. 3 are optical microscopic photographs,showing typical microstructures. FIG. 1 is an optical microscopicphotograph, showing the microstructure of a composite material in whichaluminum alloy A5005 penetrated and solidified in a plated fine particlematerial (alumina having the average particle size of 50 μm). FIG. 2 isan optical microscopic photograph, showing the microstructure of acomposite material relating to the present invention in which aluminumalloy A5005 penetrated and solidified in particles where a plated fineparticle material (alumina having the average particle size of 50 μm)and a non-plated fine particle material (alumina having the averageparticle size of 50 μm) were mixed at 2:1. FIG. 3 is an opticalmicroscopic photograph, showing the microstructure of a compositematerial relating to the present invention in which aluminum alloy A5005penetrated and solidified in particles where a plated fine particlematerial (alumina having the average particle size of 50 μm) and anon-plated fine particle material (alumina having the average particlesize of 50 μm) were mixed at 1:2. TABLE 1 Coefficient Plating Mixingratio of thermal Young's Yield Matrix thickness of plated expansionmodulus strength alloy (μm) particles (%) (×10⁻⁶) (GPa) (MPa)Penetration A1050 0.3 100 13.4 54 33 Partially difficult to penetrateA1050 0.3 67 13.5 — — Partially difficult to penetrate A1050 0.3 50 — —— Difficult to penetrate A1050 0.3 33 — — — Difficult to penetrate A50050.3 100 13.3 110 72 Good A5005 0.3 67 13.2 95 69 Good A5005 0.3 50 13.555 44 Good A5005 0.3 33 13.4 45 39 Good

Example 2

[0035] Alumina that was Ni-plated at the thickness of 0.3 μm on thesurface of particles and had the average particle size of 50 μm, andalumina that was not surface treated and had the average particle sizeof 50 μm, were mixed at the ratio of 2:1. Dispersion particles mixed atthe ratio were filled in a graphite jig. Subsequently, pure aluminumA1050 (Al>99.5%) or aluminum-magnesium alloy (Al-0.18 to 2.308Mg)arranged on the particles melted, penetrated without pressure, andsolidified, thus providing a composite material as a sample. Themechanical and physical characteristics of the sample are shown in Table2. In Table 2, the degree of penetration was determined by whether ornot molten metal penetrated evenly to the degree of penetration wasdetermined by whether or not molten metal penetrated evenly to thicknessof the layer of the dispersion particles filled in the jig. TABLE 2Mixing ratio Plating of plated Young's Yield thickness particles Pene-modulus strength Matrix alloy (μm) (%) tration (GPa) (MPa) Al (>99.5)0.3 67 Difficult — — to penetrate Al - 0.18 Mg 0.3 67 Difficult — — topenetrate Al - 0.41 Mg 0.3 67 Good 83 63 Al - 0.62 Mg 0.3 67 Good 89 66Al - 0.81 Mg 0.3 67 Good 95 69 Al - 1.08 Mg 0.3 67 Good 104 72 Al - 2.30Mg 0.3 67 Good 122 84

[0036] Clearly shown in the above-noted results, impregnationcharacteristics improve with the increase in the amount of added Mg.This is because Mg effectively reduces solid-liquid surface energy asshown above.

[0037] The porous metal based composite material relating to the presentinvention is a superior composite material that can be manufacturedwhile mechanical and physical characteristics such as coefficients ofthermal expansion, Young's modulus and proof stress are effectivelycontrolled at preferable levels by a simple control. Moreover, theporous metal based composite material relating to the present inventionis reliable, with no damage, since stress among materials is reduced, sothat an excellent composite material can be provided.

What is claimed is:
 1. A porous metal based composite materialcomprising a metal material for forming a matrix, and at least two kindsof fine particle materials having different wettabilities with respectto the metal material; said porous metal based composite material beingprovided by melting and impregnating the metal material to a mixture ofthe at least two kinds of fine particle materials.
 2. The porous metalbased composite material according to claim 1, wherein the metalmaterial for forming a matrix is Au, Ag, Cu, Pd, Al, Fe, Cr, Co or Ni,or an alloy containing these metals as a main component; and wherein themixture of the at least two kinds of fine particle materials havingdifferent wettabilities with respect to the metal material is a mixtureof surface treated ceramic fine particles, cermet fine particles ormetal fine particles, and surface untreated ceramic fine particles,cermet fine particles or metal fine particles.
 3. The porous metal basedcomposite material according to claim 1, wherein the mixture of the atleast two kinds of fine particle materials having differentwettabilities with respect to the metal material contains the surfaceuntreated fine particles and the surface treated fine particles at avolume mixing ratio of 80:20 to 5:95.
 4. The porous metal basedcomposite material according to claim 2, wherein the mixture of the atleast two kinds of fine particle materials having differentwettabilities with respect to the metal material contains the surfaceuntreated fine particles and the surface treated fine particles at avolume mixing ratio of 80:20 to 5:95.